The present invention relates generally to a pattern recognition system that handles image imputs from a TV camera, such as characters and figures, and specifically it pertains to the art that allows unidentified characters or graphical figures to be recognized by first converting the image input into a binary signal form composed of black and white intensity levels to obtain its input image pattern, and then matching the thus obtained image pattern against a reference pattern previously defined and stored in memory, e. g. in the form of a dictionary file. More specifically, the present invention relates to a method of and an apparatus for tracking the outline of a pattern whereby the outer contours or boundaries of an object can be traced by a high-rate scanning prior to the required pattern matching operation.
Usually, this type of pattern outline tracking, whose principle of operation is illustrated in FIG. 1, takes place by first scanning through the image or picture memory in which a given input pattern is stored in the direction of the scan lines as indicated by an arrow a, finding out any point S1 that satisfies the specific conditions in order to be used as the starting point of the outer contour of the image, and then beginning to trace the outer contour of the input pattern with the thus found starting point S1 (as shown by an arrow b in the same figure). Following the above first scanning, another scanning is then repeated to find the starting point S2 next to be traced. If found, the tracking begins with the new starting point. Then, the same procedure is repeated successively until all possible starting points to be traced are found, and is completed when no more starting points can be found.
As it may readily be understood from the above description, when the above tracking system is used and if an input pattern contains a large number of outlines, it would be necessary to find the starting points to be traced for all the outlines, and accordingly to scan through the image memory from the top address to the bottom address repeatedly each time an attempt is made to find those starting points. During the outline tracking process, therefore, the time required for finding the starting points would be considerably increased, which causes a reduction in the performance in the outline tracking, or even the total processing efficiency in the pattern recognition.